1. Field of the Invention
The present invention relates to a fuel tank composed of a thermoplastic synthetic resin and, more particularly, to a fuel tank having built-in parts and valves with tubes, of which an outer wall is formed by subjecting a thermoplastic synthetic resin member to blow molding.
2. Description of Related Art
Conventionally, fuel tanks for motor vehicles, etc. have been formed of metal. But, recently, fuel tanks formed of a thermoplastic synthetic resin have been frequently used, because it is lightweight, free from rust, and readily formed into a desired configuration.
In many cases, the fuel tanks formed of thermoplastic synthetic resin have been produced with the blow molding method, because tubular bodies can be readily formed therewith. With the blow molding method, a cylindrical-shaped parison composed of a molten synthetic resin is extruded into a mold from the upper side thereof, and air is blown into the parison while holding the parison with the mold.
On the other hand, upon blow molding, there are the cases where fuel gas generated inside the fuel tank must be discharged outside thereof, and air must be introduced inside thereof, because the inside pressure of the fuel tank becomes negative. In such cases, in order to prevent fuel that is liquid from flowing out of the fuel tank, valves have been provided inside the fuel tank, along with tubes and discharge holes adapted to discharge gas outwardly.
As shown in FIG. 1, in order to discharge gas, tubes 10 having valve units 12 and baffle plates 14 are provided within a fuel tank 16 made of metal (see publication of unexamined Japanese patent application No. 2006-264372, for example.).
Since the fuel tank 16 is made of metal so that the tubes, etc. are held with holding members provided inside the fuel tank by welding, but it has been difficult to provide holding members inside the fuel tank composed of a synthetic resin, which has been made with blow molding.
And, as shown in FIG. 2, in order to provide a fuel pump 18 and a valve 20 within a fuel tank 22, a synthetic resin plate 24 to which the fuel pump 18 and the valve 20 are attached is inserted in a parison 26, and the synthetic resin plate 24 held with the parison 26 is subjected to blow molding, and as a result, the fuel pump 18 and the valve 20 are attached within the fuel tank 22 (see publication of unexamined Japanese patent application No. Hei1-301227, for example.).
In this case, the synthetic resin plate 24 to which the fuel pump and valves are attached is fixed to a resin frame and secured to an inner surface of an outer wall of the fuel tank so as to require a detaching step of the resin frame after blow molding. Accordingly, it has been demanded to secure the fuel pump and valves to the outer wall of the fuel tank directly, and form an outlet hole, and consequently, the construction of the synthetic resin plate 24 becomes complicated, whereby the attaching positions of the fuel pump and valves are also limited to specific positions.
On the other hand, there are the cases where a built-in part having column members adapted to increase the strength of the fuel tank upon blow molding is provided therein (see publication of unexamined Japanese patent application No. Hei6-143396, for example.).
In this case, however, where valves, tubes, etc. are attached to the built-in part, the tubes may contact a molten parison during blow molding because the tubes attached to the valves exhibit flexibility, and as a result, the tubes may be adhered to the parison. And, dust and dirt may intrude into tubes during the molding step, and consequently, caps must be attached to open ends of the tubes, thereby decreasing the productivity.